The voltage-gated K+ channels define a class of 6-TM channels that open and close in response to changes in the membrane potential. They are functionally and structurally similar to voltage-gated Na+ and Ca++ channels and share a similar transmembrane architecture with cyclic nucleotide gated (CNG) channels, the pacemaker channels (HCN) of the heart, and transient receptor potential (TRP) channels involved in heat and pain sensation. The goal of the proposed research is to structurally define the open and closed state of a voltage-gated K+ channel. We will employ X-ray crystallography to solve high resolution structures of channels trapped in distinct conformations. Trapping will be accomplished through point mutations and engineered covalent cross-links between portions of the protein known to move relative to each other. The biological relevance of our structures will be assessed by comparing the X-ray structures to independent models we will determine using electrophysiology and fluorescence spectroscopy. [unreadable] [unreadable]